Fix LIVE open/close double-book and security audit findings.

Prevent expiry dual-close from re-booking option cash, abandon ledger rejection, margin-mode mismatch, and manual close races; harden fill wait and refuse default AUTH_SECRET on LIVE.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/main.py

@@ -36,6 +36,14 @@ async def lifespan(app: FastAPI):
     # 而 health 显示 DB 里的 binance → 合约号/盘口错乱（期权一直 -/-）
     from .exchange.runtime import load_runtime_settings
 
+    app_settings = get_settings()
+    if not app_settings.is_sim:
+        secret = (app_settings.auth_secret or "").strip()
+        if not secret or secret == "change-me-eth-hedge-sim-secret":
+            raise RuntimeError(
+                "LIVE 拒绝启动：请在 .env 设置非默认 AUTH_SECRET（勿用 change-me-eth-hedge-sim-secret）"
+            )
+
     settings = load_runtime_settings()
     engine = StrategyEngine()
     set_engine(engine)